Inhibitors of dipeptidylpeptidase IV, also DPP-IV inhibitors or gliptins, are a class of oral hypoglycemics that block DPP-IV. They can be used to treat diabetes mellitus type 2.
Linagliptin, which is chemically known as 8-[3(R)-Aminopiperidin-1-yl]-7-(2-butynyl)-3-methyl-1-(4-methylquinazolin-2-ylmethyl)xanthine, is represented by compound of Formula I.

TRADJENTA® is Boheringer's (R)-linagliptin 5 mg once daily tablet indicated for type 2 diabetes mellitus as an adjunct to diet and exercise.
Alogliptin chemically known as 2-[6-[3(R)-Aminopiperidin-1-yl]-3-methyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-ylmethyl]benzonitrile is represented by the structural formula, shown below

Alogliptin is a dipeptidylpeptidase IV (DPP4) inhibitor approved in Japan for monotherapy and in combination with an alpha-glucosidase inhibitor for the once-daily, oral treatment of type 2 diabetes.
U.S. Pat. No. 7,407,955 (US Pat. '955) discloses linagliptin and process for preparing it. US Pat. '955 discloses process for preparing linagliptin by deprotecting N-BOC protected linagliptin.

Presently, we have developed a novel process for the preparation of linagliptin which involves deprotecting a compound of Formula II.
wherein R1 and R2 together with the nitrogen to which they are attached form a phthalimido group, wherein the aromatic ring of the phthalimido group is substituted with one or more R3 substituents selected from the group consisting of halogen, alkyl, nitro and amino; or R1 is H and R2 is selected from the group consisting of trialkylsilyl, 2-trialkylsilylethoxycarbamates, acetyl, trihaloacetyl, 9-fluorenylmethoxycarbonyl, trityl, alkylsulfonyl, arylsulfonyl, diphenylphosphine and sulfonylethoxycarbonyl.
The process of the present invention is novel, commercially advantageous and industrially feasible and leads to the formation of linagliptin in higher yields and purity as compared to the known process.